But when it comes to caffeine intake, teenagers seem to be getting far more caffeine from coffee drinks.

A new report, published in the journal Pediatrics, finds that 17- and 18-year-olds are consuming almost double the amount of caffeine from coffee compared with a decade earlier. And increasingly, younger tweens and teens, ages 12-16, are getting more caffeine from coffee, too.

"It was a surprise," researcher Amy Branum, of the Centers for Disease Control and Prevention, told us about the uptick in coffee. She's the lead author of the paper, which compared consumption in 2000 and 2010.

But interestingly, Branum says that over that time period, caffeine consumption overall has remained about the same. So, does this mean adolescents must be drinking less of other types of caffeinated drinks? Turns out, yes. Consumption of caffeinated sodas like Coke and Pepsi is down about 40 percent among older teens.

And while energy drink consumption did increase during the period, Branum and her colleagues found that the drinks account for just a small sliver of overall caffeine consumption. Among 17- and 18-year-olds, it's less than 5 percent of their caffeine consumption.

College-aged young adults (ages 19 to 22) appear to be the more regular consumers of energy drinks, but they're still only getting about 10 percent of their caffeine from this source.

Now, as we've reported, adolescents are not always aware of how much caffeine they're drinking. Especially when they're new to the coffee habit.

The Center for Science in the Public Interest took a look at several popular items and analyzed their caffeine content. It found that a 12-ounce cup of coffee from Starbucks contains about 260 milligrams of caffeine, which is roughly five times as much as a 12-ounce can of Diet Coke. And data from the University of Florida show just how much caffeine variation there can be in coffee drinks.

Other interesting findings from the Pediatrics study:

About three-fourths of children in the U.S. consume caffeine on a given day.

The preschool set, which seems to be introduced to caffeine via soda, tea or chocolate-flavored milk, is consuming a little less caffeine compared with a decade ago.

On average, preschool-aged kids are consuming about 10 milligrams of caffeine a day. That's equivalent to less than one-third of a can of caffeinated cola.